The fastest pace of reduction was in the 1990s. A deceleration began just before the new century started, and there has been a further easing of the pace in the past six years. Nevertheless, year by year, the number continues to fall.

By the start of 2018 the global total of nuclear weapons was 14 700 compared with an all-time high of some 70 000 in the mid-1980s. While nuclear weapons are more capable in many ways than before, the reduction is, nonetheless, both large and significant.

Cracks appear: Charge and counter-charge

Even while the number continued to drop, problems were emerging. Not least, in 2002 the USA unilaterally withdrew from the ABM Treaty. However, that did not stop Russia and the USA from signing the Strategic Offensive Reductions Treaty (SORT Treaty) in 2002 and New START in 2010, but perhaps it presaged later developments.

Thus, the allegation that Russia has breached the INF Treaty is, in other words, not new. This year the USA’s NATO allies also aligned themselves with the US accusation, albeit somewhat guardedly (note the careful wording in paragraph 46 of the July Summit Declaration).

The charge is that Russia has developed a ground-launched cruise missile with a range over 500 kilometres. Many details have not been clearly stated publicly, but it seems Russia may have modified a sea-launched missile (the Kalibr) and combined it with a mobile ground-based launcher (the Iskander K system). The modified system is sometimes known as the 9M729, the SSC-8 or the SSC-X-8.

Russia rejects the US accusation. It makes the counter-charge that the USA has itself violated the INF Treaty in three ways: first by using missiles banned under the treaty for target practice; second by deploying some drones that are effectively cruise missiles; and third by taking a maritime missile defence system and basing it on land (Aegis Ashore) although its launch tubes could, the Russians say, be used for intermediate range missiles. Naturally, the USA rejects these charges.

A further Russian criticism of the USA over the INF Treaty is that, if the USA wanted to discuss alleged non-compliance, it should have used the treaty’s Special Verification Commission before going public.

This was designed specifically to address questions about each side’s compliance. The Commission did not meet between 2003 and November 2016, and it was during that 13-year interval that US concerns about Russian cruise missiles emerged.

Now Trump seems to have closed the argument by announcing withdrawal. Under Article XV of the treaty, withdrawal can happen after six months’ notice. Unless there is a timely change of approach by either side or both, the INF Treaty looks likely to be a dead letter by April 2019.

It could be, however, that the announcement is intended as a manoeuvre to obtain Russian concessions on the alleged missile deployment or on other aspects of an increasingly tense Russian–US relationship. That is what Russian deputy foreign minister, Sergey Ryabkov, implied by calling the move ‘blackmail’.

Arms control in trouble

Whether the imminence of the INF Treaty’s demise is more apparent than real, its plight is part of a bigger picture. Arms control is in deep trouble. As well as the US abrogation of the ABM Treaty in 2002, • Russia effectively withdrew from the CFE Treaty in 2015, arguing that the equal cap was no longer fair after five former WTO states joined NATO; • The 2010 New START agreement on strategic nuclear arms lasts until 2021, and there are currently no talks about prolonging or replacing it; and • Russia claims that the USA is technically violating New START because some US launchers have been converted to non-nuclear use in a way that is not visible to Russia.

As a result, Russia cannot verify them in the way the treaty says it must be able to. The Russian Government’s position is that until this is resolved, it is not possible to start work on prolonging New START, despite its imminent expiry date.

It seems likely that the precarious situation of Russian–US arms control will simultaneously put increasing pressure on the overall nuclear non-proliferation regime and sharpen the arguments about the 2017 Treaty on the Prohibition of Nuclear Weapons (TPNW, or the Nuclear Weapon Ban Treaty).

For the advocates of what is often known as the nuclear ban, the erosion of arms control reinforces the case for moving forward to a world without nuclear weapons. For its opponents, the erosion of arms control shows the world is not at all ready for or capable of a nuclear ban.

The risk of a return to nuclear weapon build-ups by both Russia and the USA is clear. With it, the degree of safety gained with the end of the cold war and enjoyed since then is at risk of being lost. Aware of the well-earned reputation for springing surprises that the Russian and US presidents both have, there may be more developments in one direction or another in the coming weeks or even days.